The invention relates to an apparatus for the electroplating of metal strips, and more particularly for the zinc-coating of steel strip, which comprises a tank that is filled with electrolytic liquid which, in particular, flows therethrough; at least one electrode disposed above the strip; and at least one electrode disposed below the strip, both being parallel thereto and immersed in the electrolytic liquid.
In a known apparatus of this type (German Pat. No. 689,548), an electrode made of the metal to be deposited is provided only on the side of the strip which it is desired to coat; and when both sides of the strip are to be coated, electrodes made of the metal to be deposited are disposed on both sides of the strip. The depositable metal of the electrode is consumed in the course of the electroplating operation, and as a result of the attendant change in the distance between the side of the strip being coated and the electrode the electric field changes. Thus there is no assurance that electroplating will be uniform over the entire length of the strip. If more or less uniform electroplating were to be secured with this apparatus, the electrodes would have to be replaced at regular intervals. Now such replacement, especially of the electrode located below the strip, is difficult and time-consuming and requires that the apparatus be shut down.
Difficulties of this type have not been encountered with an earlier apparatus which has again been attracting attention of late. (German Pat. No. 250,403; Stahl und Eisen 92 [1972], No. 18, page 833.) In that apparatus the anode is formed of an insoluble metal, which means that the initial spacing remains unchanged even during extended operation. However, to avoid a drop in the ion transport, necessary to electroplating, in the electrolyte, the electrolytic liquid must be worked up in separate, additional equipment in such a way that it contains ions of the metal to be deposited in sufficient concentration. In other words, in this apparatus the electrolyte must be continuously recirculated between the coating apparatus and the working-up equipment.